1. Field of the Invention
This invention relates to a distance measuring apparatus adapted for automatic focusing in compact equipment such as a camera and more particularly to an input circuit for apparatus in which an energy such as light is projected from a light projecting part onto a distance measuring object. Then reflection energy reflected by the object is received by a plurality of sensor elements arranged away from the light projecting part by a base length, and the outputs of these sensor elements are computed to obtain the distance to the object.
2. Description of the Prior Art
Known distance measuring methods include a light irradiating type called the light active, trigonometric distance measuring method in which light is projected from a light projecting part onto the distance measuring object and a reflection light reflected by the object as a result of the light projection is received by a light receiving part disposed away from the light projecting part by a predetermined base length. The methods also include a trigonometric distance measuring method called the active type. For these distance measuring methods, there have been proposed and actually employed various methods for eliminating the necessity of a moving part by means of a plurality of sensor elements. These methods are advantageous in that distance information is obtainable prior to a photo-taking operation. However, these known methods have the following shortcoming: In these prior art methods, as typically seen in Japanese Patent Application Laid-Open No. SHO 56-29110, an input circuit includes the same number of amplifiers as the photo-sensitive elements for processing the outputs of these elements by comparing and computing them. This necessitates expansion of the circuit arrangement scale. Although advancement in the integrated circuit technology makes such a large circuit arrangement feasible, it inevitably results in a complex structural arrangement and an increase in cost.
On the other hand, to reduce the circuit arrangement scale, a method for distance measurements has also been proposed in which, as disclosed in Japanese Utility Model Publications Nos. SHO 55-2401 and SHO 56-11051, two light sensitive elements are either parallel or series connected in opposite directions in such a manner as to offset the output currents of these elements and to measure the object distance by obtaining the difference between them. In this case, however, what is obtainable is limited to difference information, while absolute distance information is barely obtainable. Such a method thus necessitates the auxiliary use of a moving part such as a servo mechanism.